Mill systems for processing dehydrated forage crops are, of course, well known in the art. Such systems are employed to convert dried leafy material into pellet form for ease of handling and storage. These systems typically include a hammer mill for comminuting the dried crop material, a pellet mill for forming pellets from the pulverized material, and a pellet cooler for firming hot fragile pellets produced by the pellet mill to minimize pellet breakage and the formation of fines.
A problem with crop material processing systems heretofore available has been the undesired deterioration of the hot pellets into fines during conveyance from the pellet mill to the cooler and during the cooling cycle itself. In this regard, the size of these mill systems is typically of such magnitude that the pellet cooler is necessarily spaced remote from the pellet mill thereby requiring that the hot pellets from the mill be conveyed (generally by pneumatic means) an appreciable distance prior to cooling. Inasmuch as the hot pellets are relatively fragile, significant erosion and deterioration of the pellets occurs during conveyance between the pellet mill and the cooler resulting in the production of appreciable amounts of fines (small dust like particles of crop material). These fines are undesirable for animal consumption and moreover, they present burdensome material handling and storage problems; hence, the typical practice is to provide means for drawing off fines and recycling them through the pellet mill. This process, of course, reduces the overall efficiency of the pellet cooler and thereby increases the operating cost of the mill system.
Even in systems where the pellet cooler is located in proximity to the pellet mill, undesirable amounts of fines may be produced by virtue of the nature of the operation of the pellet cooler. In this connection, coolers suitable for use in such systems must be capable of rapidly cooling relatively large amounts of material in pellet form. Typically such coolers comprise a ventilated tank into which pellet material is gravity fed and stored while ambient air is circulated through the material for cooling. See for example U.S. Pat. No. 3,289,568 issued Dec. 6, 1966. Though such coolers are highly desirable from the standpoint of economical operation, there may be produced significant amounts of fines in these coolers due to tumbling and interaction of the pellets as they are fed into the cooler and subjected to the cooling air currents.